Detection of picosecond magnetization dynamics of 50 nm magnetic dots down to the single dot regime

We report an all-optical time-domain detection of picosecond magnetization dynamics of arrays of 50 nm Ni80Fe20 (permalloy) dots down to the single nanodot regime. In the single nanodot regime the dynamics reveals one dominant resonant mode corresponding to the edge mode of the 50 nm dot with slightly higher damping than that of the unpatterned thin film. With the increase in areal density of the array both the precession frequency and damping increases significantly due to the increase in magnetostatic interactions between the nanodots and a mode splitting and sudden jump in apparent damping are observed at an edge-to-edge separation of 50 nm.

All-Optical Excitation and Detection of Picosecond Dynamics of Ordered Arrays of Nanomagnets with Varying Areal Density

We have demonstrated optical excitation and detection of collective precessional dynamics in arrays of coupled Ni80Fe20 (permalloy) nanoelements with systematically varying areal density by an all-optical time-resolved Kerr microscope. We have applied this technique to precisely determine three different collective regimes in these arrays. At very high areal density, a single uniform collective mode is observed where the edge modes of the constituent elements are suppressed. At intermediate areal densities, three nonuniform collective modes appear and at very low areal density, we observe noncollective dynamics and only the centre and edge modes of the constituent elements appear.